The invention relates to wax crystal modifiers useful in improving the flow characteristics of lube oils and waxy crudes.
Many oils, especially crude oils, contain straight chain and branched alkanes that crystallize as their temperature is lowered. Alkane (wax) crystallization in these oils results in increased viscosity which leads to problems such as pipelining difficulties in crudes. The temperature at which wax begins to crystallize in an oil is called the wax appearance temperature (WAT) of the oil. Polymeric and copolymeric compounds can be combined with an oil in order to reduce an oil""s WAT. Such additives, known as wax crystal modifiers, can be used as flow improvers in lubricating oils.
Lubricating oils and crude oils have quite different compositions. For example, crude oils contain inorganics, resins, and asphaltenes that are not present in lubricating oils beyond trace levels. Crude oils also contain hydrocarbons having a wider range of molecular weights. These factors contribute to a higher WAT than in lubricating oils. Crude oil WATs can range from about xe2x88x9215xc2x0 C. to about 30xc2x0 C., compared to a range of about xe2x88x9225xc2x0 C. to about xe2x88x925xc2x0 C. for lubricating oils.
Dialkyl fumarate-vinyl acetate (DAF-VA) copolymers are used as lubricating oil flow improvers. These copolymers may be formed by the free radical polymerization of vinyl acetate and DAF esters having alkyls ranging in size from about 10 to about 18 carbon atoms. Such copolymers are effective lubricating oil flow improvers at temperatures ranging from about xe2x88x9225xc2x0 C. to about xe2x88x925xc2x0xc2x0 C. Such flow improvers are not expected to be effective for crude oils because crude oil WATs are generally outside this temperature range.
There remains a need for polymers and copolymers useful for improving the flow properties of oils, and especially polymers and copolymers capable of improving the flow properties and pipelinability of crude oils.
In one embodiment, the invention is a copolymer of carbon monoxide and C6 to C250 straight-chain or branched dialkyl fumarate.
In another embodiment, the invention is a flow improver for use in an oleaginous fluid comprising one or more copolymers of dialkyl fumarate wherein the alkyl is straight chain or branched and ranges in size from C6 to C250 and carbon monoxide.
In another embodiment, the invention is a crude oil wax crystal modifier comprising a copolymer of dialkyl fumarate having straight chain or branched alkyls ranging in size from about C6 to about C250 and at least one compound selected from the group consisting of C3 to C30 alpha olefin, ethylene, styrene, carbon monoxide, and vinyl acetate.
In another embodiment, the invention is a method for improving the flow properties in an oleagenous fluid comprising: adding to a major amount of the oleagenous fluid a minor amount of at least one copolymer of dialkyl-fumarate having C6 to C250 straight chain or branched alkyls and at least one compound selected from the group consisting of C3 to C30 alpha olefin, ethylene, styrene, and carbon monoxide, provided that when the oleagenous fluid is a lubricating oil or a distillate oil that the compound is carbon monoxide.
In another embodiment, the invention is a method for forming a copolymer comprising:
dissolving a C6 to C250 straight-chain dialkyl fumarate in a solvent selected from the group consisting of hexane, benzene, cyclohexane, chloroform, xylene, oil, and heptane;
combining the dissolved dialkyl fumarate and an initiator selected from the group consisting of t-butyl peroxypivalate, benzoyl peroxide, t-butylper benzoate, and t-butyl peroxide in a reactor;
sealing the reactor and then purging the reactor with purified nitrogen;
pressurizing the reactor with at least one compound selected from the group consisting of carbon monoxide and ethylene to a pressure ranging from about 100 to about 3000 psig; and
heating the reactor to a temperature ranging from about 40xc2x0 C. to about 200xc2x0 C. for a time ranging from about 1 hour to about 48 hours in order to form the copolymer.
In another embodiment, the invention is a method for forming a copolymer comprising:
combining under free radical polymerization conditions a C6 to C250 straight-chain dialkyl fumarate in a solvent selected from the group consisting of hexane, benzene, cyclohexane, chloroform, xylene, oil, and heptane; at least one compound selected from the group consisting of ethylene and carbon monoxide; and an initiator selected from the group consisting of t-butyl peroxypivalate, benzoyl peroxide, t-butylper benzoate, and t-butyl peroxide, for a time, temperature, and pressure sufficient to form the copolymer.
In another embodiment, the invention is a method for improving the flow properties in an oleagenous fluid having at least one alkane species comprising:
determining a molecular weight distribution of the alkane species in the oleagenous fluid and then
adding to a major amount of the oleagenous fluid a minor amount of at least one copolymer of dialkylfumarate having straight chain or branched alkyls having substantially the same molecular weight distribution and at least one compound selected from the group consisting of C3 to C30 alpha olefin, ethylene, styrene, and carbon monoxide.
The invention is based on the discovery that dialkylfumarate-containing copolymers having straight chain or branched alkyls ranging in size from about C6 to about C250 are effective flow improvers in oleaginous fluids such as fuel oils, lubricating oils, and crude oils. The invention is also based on the discovery that dialkylfumarate can be copolymerized with carbon monoxide.
Copolymers of the present invention having the formula: 
wherein B is formed from compounds selected from the group consisting of carbon monoxide, vinyl acetate, styrene, ethylene, and C3 to C30 alpha olefin and wherein R is branched or straight chain alkyl ranging from C6 to C250 are prepared as follows.
Dialkylfumarate esters having alkyls ranging up to C250 are prepared by diesterification of fumaric acid with aliphatic alcohols in the presence of a p-toluene sulfonic acid catalyst. Alternatively, the esters can be prepared from fumaryl chloride and alkyl alcohols using an amine catalyst.
Comonomer B is formed from at least one compound selected from the group consisting of vinyl acetate, styrene, C3 to C30 xcex1-olefin, ethylene, and carbon monoxide. The term copolymer is thus used in accordance with its more general meaning where the polymer comprises two or more different monomers.
R represents independently selected straight chain or branched alkyl groups of from about C6 to about C250 carbon atoms. Preferred alkyls range from about C8 to about C40.
The copolymers of this invention can be synthesized using free-radical polymerization. In the case of copolymers of dialkyl fumarate with monomers like vinyl acetate, styrene or C3 to C30 xcex1-olefins, polymerization can be carried out in a standard glass reactor. Typically, any inhibitors present in the monomers are removed via an inhibitor remover column. The purified monomers are then placed in tubes with the DAF ester monomers. The tubes are capped with septa and flushed with nitrogen for one to four hours before polymerization. The composition of monomers can be varied from about 5:95 to about 95:5 mole percent.
The reactions can be carried out in a solvent or neat. When a solvent is used, the solvent should be nonreactive or noninterfering in free radical polymerization. Such solvents include benzene, cyclohexane, hexane, heptane, etc. Solvents like xylene or oil can also be used. The solvent may be flushed with argon or nitrogen and then added to the monomers.
The polymerization reactions can be carried out from 40 to 100xc2x0 C. depending on reactivity of monomers, half-life of the initiator used, or the boiling point of the solvent. The reactions are carried out under inert atmosphere. The solvents are brought to the reaction temperatures, and the initiator (dissolved in the appropriate solvents) is added to the solution. Typical free radical initiators includes dialkyl peroxides such as ditertiary-butyl peroxide, 2,5-dimethyl-2,5-di-tertiary-butylperoxyhexane, di-cumyl peroxide; alkyl peroxides such as benzoyl peroxide; peroxy esters such as tertiary-butyl peroxypivalate, tertiary-butyl perbenzoate; and also compounds such as azo-bis-isobutyronitrile. A free radical initiator with an appropriate half life at reaction temperature of from about 60xc2x0 C. to about 140xc2x0 C. can be used. For the reactions done neat (without solvent), both monomers and initiator are loaded together, flushed with nitrogen, and then brought to reaction temperature. The components are stirred for a time sufficient to form a uniform mixture.
Reaction time ranges from about 1 hour to about 48 hours. The resulting polymer is isolated by precipitating the polymer in non-solvent (solvent in which polymer is not soluble). The product is then dried in vacuum oven.
When forming the compounds of the present invention from monomers that are gases at ambient temperature and pressure, such as ethylene and carbon monoxide, the reactions are generally carried out in high pressure reactors such as autoclave reactors. In such copolymerizations, the reactor is initially charged with monomers like dialkyl fumarate dissolved in a solvent such as hexane, and initiator is added. Typical initiators include t-butyl peroxypivalate, benzoyl peroxide, t-butylper benzoate, t-butyl peroxide. The reactor is sealed and purged with purified nitrogen. The reactor is then pressurized with carbon monoxide and/or ethylene monomer to appropriate pressure. The pressure can range from about 100 to about 3,000 psig. The preferred polymerization pressure ranges from about 500 to about 1,200 psig. Reaction temperature can range from about 40xc2x0 C. to about 200xc2x0 C., depending on solvent and the initiator half-life. The pressure of the reaction can be maintained for about one hour to about 48 hours depending on monomer reactivity, solvent, and the initiator half-life. The reactor is allowed to cool to room temperature and is then depressurized. A rotary evaporator is used to remove the solvent and obtain the product.
The products are generally characterized by standard techniques such as FTIR, NMR, and GPC.
According to the present invention, wax crystal modifiers are added to an oleaginous fluid such as oil in a concentration ranging from about 10 to about 50,000 ppm based on the weight of the oil. The preferred concentration is about 500 ppm. Non-limiting examples of oleaginous fluids containing paraffinic (alkane) species that benefit from the addition of the compounds of the invention include crude oils, i.e., oils as obtained from drilling and before refining or separating, fuel oils such as middle distillate fuel oil, and oils of lubricating viscosity (xe2x80x9clubricating oilsxe2x80x9d).
It is believed that copolymer flow improvers of this invention when present in an effective amount are capable of inhibiting the nucleation and growth of wax crystals in oleaginous fluids such as oils. While not wishing to be bound by any theory, it is believed that the presence of an effective amount of copolymer results in a lowering the oil""s wax appearance temperature because the copolymer molecules are sufficiently similar to the paraffinic crude species to incorporate themselves into growing wax crystals. Once incorporated, it is believed that the polymeric nature of the flow improver, i.e., its xe2x80x9cbranchinessxe2x80x9d and high molecular weight, prevent the further addition of the crude""s paraffinic species to the crystal. The presence of the copolymer in the growing wax crystal is also believed to alter the crystals"" morphology by inhibiting growth that naturally tends towards undesirable large flat platelets. Such platelets are believed to result from the interlocking, intergrowth, and agglomeration of nucleated wax crystallites. Such changes in crystal shape resulting from copolymer incorporation greatly diminish the wax crystals"" ability to interlock, intergrow, and agglomerate.
In the practice of the invention, it is desirable to first determine the molecular weight distribution of the paraffinic species present in the oil. It is believed that the compounds of the present invention are most effective when the molecular weight distribution of the alkyls present in the fumaric species of the copolymer is approximately the same as the molecular weight distribution of the oil""s paraffinic species.
While the compounds of the present invention are useful in all oleaginous fluids containing paraffinic species, the preferred compound will depend on the type of fluid used.
For lubricating oils, for example, flow improvement is needed at temperatures much lower than are ordinarily required for crude oil. Consequently, copolymers with alkyls in the fumarate species ranging from about C12 to about C14 and molecular weights ranging from about 2000 to about 100,000 are preferred. In crude oils, compounds of reduced solubility are required, and the preferred compounds contain alkyls ranging from about C15 to about C40 and molecular weights ranging from about 2,000 to about 50,000. For distillate oils, preferred copolymers contain alkyls ranging from about C10 to about C22 and have molecular weights ranging from about 2,000 to about 20,000.